1 Image Processing : 1. Camera Models 1. Camera Models Aleix M. Martinez [email protected]Why Camera Modeling? • Think it this way: You look at the world trough the lens of a camera and take a picture. WORLD CAMERA PICTURE • Now you show the photo to a friend. S/he needs to interpret the image; i.e., WORLD CAMERA PICTURE MODEL Definition : A camera is an imaging device that captures light and imprints it into a translucent plate (which is usually located at the back of the device). Another applications of camera modeling: Rendering • Imagine you want to superimpose a graphic animation on top of a football field. To be able to draw the projection of a 3D object on a 2D image of a 3D surface, you first need to recover the 3D parameters of the “world.” • This is known as rendering.

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2 What do we need to do, then? • In this part of the course, we will formulate the most useful model: the pinhole camera . • Pinhole cameras can be modeled using two main types of projections: – Prespective projection. – Affine projections. • These do not consider lenses. These are more difficult to model and not as useful. Pinhole Cameras This is the actual picture This is the same image , rectified and normalized. They are formed by the projection of 3D objects. Perspective Projection • We now know what a pinhole camera is. •Let’s see how we can model the projection of a 3D world point to a 2D image point. • We will start defining the most realistic projection. • Later, we will define simplifications of this. • Simplifications are useful for computational reasons only. Pinhole Perspective Equation NOTE: z is always negative.          z y f y z x f x ' ' ' ' You can normalize the image plane (in front of the pinhole) to solve this problem. Focal length

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